Referring to FIG. 1, the Universal Mobile Telecommunications System (UMTS) packet network architecture includes the major architectural elements of user equipment (UE), UMTS Terrestrial Radio Access Network (UTRAN), and core network (CN). The UE is interfaced to the UTRAN over a radio (Uu) interface, while the UTRAN interfaces to the core network over a (wired) Iu interface.
FIG. 2 shows some further details of the architecture, particularly the UTRAN. The UTRAN includes multiple Radio Network Subsystems (RNSs), each of which contains at least one Radio Network Controller (RNC). Each RNC may be connected to multiple NodeBs which are the UMTS counterparts to GSM base stations. Each NodeB may be in radio contact with multiple UEs via the radio interface (Uu) shown in FIG. 1. A given UE may be in radio contact with multiple NodeBs even if one or more of the NodeBs are connected to different RNCs. For instance a UEI in FIG. 2 may be in radio contact with NodeB 2 of RNS 1 and NodeB 3 of RNS 2 where NodeB 2 and NodeB 3 are neighboring NodeBs. The RNCs of different RNSs may be connected by an Iur interface which allows mobile UEs to stay in contact with both RNCs while traversing from a cell belonging to a NodeB of one RNC to a cell belonging to a NodeB of another RNC. One of the RNCs will act as the “serving” or “controlling” RNC (SRNC or CRNC) while the other will act as a “drift” RNC (DRNC). A chain of such drift RNCs can even be established to extend from a given SRNC. The multiple NodeBs will typically be neighboring NodeBs in the sense that each will be in control of neighboring cells. The mobile UEs are able to traverse the neighboring cells without having to re-establish a connection with a new NodeB because either the NodeBs are connected to a same RNC or, if they are connected to different RNCs, the RNCs are connected to each other. During such movements of a UE, it is sometimes required that radio links be added and abandoned so that the UE can always maintain at least one radio link to the UTRAN. This is called soft-handover (SHO).
The invention relates to the 3GPP (Third Generation Partnership Project) specification of the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) and more specifically to the Wideband Code Division Multiple Access (WCDMA) High Speed Uplink Packet Access (HSUPA) which is an enhanced uplink feature used in the Frequency Division Duplex (FDD) mode. This feature is being specified in the 3GPP and targeted to 3GPP release 6.
In the current architecture, the packet scheduler is located in the RNC and therefore is limited in its ability to adapt to the instantaneous traffic, because of bandwidth constraints on the Radio Resource Control (RRC) layer signalling interface between the RNC and the UE. Hence, to accommodate the variability, the packet scheduler must be conservative in allocating uplink power to take into account the influence from inactive users in the following scheduling period—a solution which turns out to be spectrally inefficient for high allocated data-rates and long release timer values.
With the introduction of HSUPA some of the the packet scheduler functionality is moved from the RNC to the NodeB. Due to the decentralization, the possibility arises to more quickly react to overload situations, enabling much more aggressive scheduling, e.g., by faster modifications of the bit rates, which will give a higher cell capacity. HSUPA and the fast NodeB controlled scheduling are also supported in soft handover.
According to Section 7.1 of the Technical Report 3GPP TR 25.896 v6.0.0 (2004-03) entitled “Feasibility Study for Enhanced Uplink for UTRA FDD (Release 6),” the term “NodeB scheduling” denotes the possibility for the NodeB to control, within the limits set by the RNC, the set of Transport Format Combinations (TFCs) from which the UE may choose a suitable TFC. In the context of HSUPA, the transport format combinations (E-TFCs) of the transport channel subject to the Node B scheduling (E-DCH) are controlled by the Node B which can grant the UE with the maximum amount of uplink resources the given UE is allowed to use. An E-TFC (E-DCH Transport Format Combination) is the combination of currently valid Transport Format for the E-DCH with the applicable maximum number of H-ARQ retransmissions and applied transmission power offset. (see 3G TS 25.309 for related definitions and in-depth explanations). In Release 5, the uplink scheduling and rate control resides in the RNC. According further to the TR 25.896 study report, by providing the NodeB with this capability, tighter control of the uplink interference is possible which, in turn, may result in increased capacity and improved coverage. The TR 25.896 report discusses two fundamental approaches to scheduling: (1) rate scheduling, where all uplink transmissions occur in parallel but at a low enough rate such that the desired noise rise at the NodeB is not exceeded, and (2) time scheduling, where theoretically only a subset of the UEs that have traffic to send are allowed to transmit at a given time, again such that the desired total noise rise at the NodeB is not exceeded. The HSUPA feature specified is expected to enable both scheduling approaches.
The present invention is related to these HSUPA enhancements of the uplink DCH (hereafter referred to as EDCH) for packet data traffic in release 6 of 3GPP as specified in the above mentioned 3GPP TR 25.896, “Feasibility Study for Enhanced Uplink for UTRA FDD” as well as in the 3GPP specification TS 25.309, “FDD Enhanced Uplink—Overall description—Stage 2,” Version 6.1.0 (2004-12). As suggested above, HSUPA enhancements are currently approached by distributing some of the packet scheduler functionality to the NodeBs. This permits faster scheduling of bursty non real-time traffic than possible using the layer 3 in the Radio Network Controller (RNC). The idea is that with faster link adaptation it is possible to more efficiently share the uplink power resource between packet data users: when packets have been transmitted from one user the scheduled resource can be made available immediately to another user. This avoids the peaked variability of noise rise, when high data rates are being allocated to users running bursty high data-rate applications.
As a consequence of much of the packet scheduler functionality having been transferred to the NodeB for EDCH, the NodeB scheduler takes care of allocating uplink resources. But it is desirable for the RNC to be able to set a certain target noise rise to the NodeB. The NodeB then takes care of scheduling such that the total noise rise level, caused by DCH and EDCH, stays below or on the target level.
The target noise rise level is set relative to the thermal plus background noise (Prx—noise). Prx—noise is therefore a reference to be used in NodeB scheduling. Prx—noise can either be measured in the NodeB directly or set by the RNC via NodeB Application Part (NBAP) signalling. Background information about measurement values can be found in 3GPP TS 25.433, Version 6.4.0 (2004-12), “UTRAN Iub Interface NBAP Signalling,” Section 9.2.1.12. Various relevant definitions can be found in 3GPP TS 25.215, Version 5.4.0 (2003-06), “Physical Layer—Measurements (FDD).”